Abstract: The low cycle fatigue (LCF) and steady cycle stress vs strain behavior of directionally solidified DZ4 superalloy at 760℃ and 800℃ are studied. Combining with the results of fracture observation, the fatigue crack initiation and propagation are analyzed. The results show that the LCF of DZ4 superalloy at 760℃ and 800℃ can be contribute to stress fatigue owing to the main elastic damage in LCF processing. The elastic damage has a favorite relativity with fatigue life. The loading frequency has an influence on steady cycle stress of DZ4 superalloy at 760℃ and especially 800℃ of all the steady cycle stress at different strain increasing with the loading frequency. The high life LCF cracks of DZ4 superalloy favorably initiate at the transverse segment of longitudinal grain boundary. And typical fatigue striation formation is difficult on fatigue crack steady propagation.

Key words: directionally solidified superalloy, low cycle fatigue, steady cycle stress, elastic damage